Automatic on/off switch for vehicle power outlets
View Patent ↗A vehicle power outlet switch ( 10 ) can include a threshold detector ( 14 ) for comparing a predetermined threshold with a vehicle battery characteristic and a power switch ( 18 ) controlled by the output of the threshold detector. Note, the vehicle battery characteristic differs while the vehicle engine is turned on or turned off and the threshold detector provides an enabling signal to the power switch when the vehicle engine is detected as being on. The threshold detector can also provide a disabling signal to the power switch when the vehicle engine is off. The power outlet switch can further include a timer ( 16 ) coupled to an output of the threshold detector that continues to provide an enabling signal to the power switch for a predetermined time after the threshold detector detects that the vehicle engine is turned off. The timer can include or be a one shot timer.
1. A vehicle power outlet switch, comprising:
a threshold detector for comparing a predetermined threshold with a vehicle battery characteristic, wherein the vehicle battery characteristic differs while the vehicle engine is turned on and while the vehicle engine is turned off;
a power switch controlled by the output of the threshold detector, wherein the threshold detector provides an enabling signal to the power switch when the vehicle engine is detected as being on;
a timer coupled to an output of the threshold detector that continues to provide an enabling signal to the power switch for a predetermined time after the threshold detector detects that the vehicle engine is turned off.
2. The vehicle power outlet switch of claim 1 , wherein the threshold detector provides a disabling signal to the power switch when the vehicle engine is off.
3. The vehicle power outlet switch of claim 1 , wherein the vehicle power outlet switch further comprises a threshold generator providing the predetermined threshold to the threshold detector, wherein the threshold generator is coupled to a vehicle battery as an input when the vehicle power outlet switch is connected to a vehicle power outlet.
4. The vehicle power outlet switch of claim 1 , wherein the vehicle power outlet switch further comprises a switch coupled to the timer that enables the timer to provide the enabling signal to the power switch for the predetermined time when the vehicle engine is turned off.
5. The vehicle power outlet switch of claim 1 , wherein the timer is a one shot timer.
6. The vehicle power outlet switch of claim 1 , wherein the predetermined threshold is a range between 12.1 volts and 15 volts.
7. The vehicle power outlet switch of claim 1 , wherein the predetermined threshold is a range between 13.8 volts and 14.2 volts.
8. The vehicle power outlet switch of claim 1 , wherein the predetermined threshold is a calculated voltage that is derived from the voltages obtained when the engine is turned on and when the engine is turned off.
9. The vehicle power outlet switch of claim 1 , wherein the vehicle power outlet switch further comprises an indicator coupled to the timer that indicates when the power switch is enabled.
10. The vehicle power outlet switch of claim 9 , wherein the indicator is selected among a visual indicator and an audible indicator.
11. A method of preventing a vehicle battery from draining when plugged to an external electronic accessory, comprising the steps of:
measuring a battery voltage at a non-switchable cigarette lighter receptacle;
comparing the battery voltage with a predetermined battery voltage to determine when a vehicle engine is off and when a vehicle engine is on; and
enabling a power switch external to the non-switchable cigarette lighter receptacle when the vehicle engine is on and disabling the power switch when the vehicle engine if off, wherein the power switch continues to be enabled for a predetermined time after determining that the vehicle engine is turned off.
12. A vehicle cigarette lighter outlet switching circuit, comprising:
a threshold detector for comparing a predetermined threshold with a vehicle battery voltage, wherein the vehicle battery voltage differs while the vehicle engine is turned on and while the vehicle engine is turned off;
an on timer that provides an enabling switch control signal at an output when the threshold detector detects the vehicle engine is on; and
a power switch controlled by the output of the on timer, wherein the on timer continues to provide an enabling signal to the power switch for a predetermined time after the threshold detector detect that the vehicle engine is turned off.
13. The vehicle cigarette lighter outlet switching circuit of claim 12 , wherein the threshold detector provides a disabling signal to the power switch when the vehicle engine is off.
14. The vehicle cigarette lighter outlet switching circuit of claim 12 , wherein the on timer continues to provide an enabling signal to the power switch for a predetermined time after the threshold detector detects that the vehicle engine is turned off.
15. The vehicle cigarette lighter outlet switching circuit of claim 14 , wherein the vehicle cigarette lighter outlet switching circuit further comprises a switch coupled to the on timer that enables the a one shot timer included within the on timer to provide the enabling signal to the power switch for the predetermined time when the vehicle engine is turned off.
16. The vehicle cigarette lighter outlet switching circuit of claim 12 , wherein the predetermined threshold is a range between 13.8 volts and 14.2 volts.
17. The vehicle cigarette lighter outlet switching circuit of claim 12 , wherein the predetermined threshold is a calculated voltage that is derived from the voltages obtained when the engine is turned on and when the engine is turned off.
18. The vehicle cigarette lighter outlet switching circuit of claim 12 , wherein the vehicle power outlet switch further comprises an indicator coupled to the on timer that indicates when the power switch is enabled.
19. The vehicle cigarette lighter outlet switching circuit of claim 12 , wherein the vehicle cigarette lighter outlet switching circuit forms a part of at least one among a power cord for an external electronic accessory or the external electronic accessory itself.